Method and apparatus for attaching power line communications to customer premises

ABSTRACT

A method and apparatus for modifying a three-phase power distribution network in a building in order to provide data communication by using a Power Line Carrier (PLC) signal to an approximate electrical central location point of the power distribution system remote from the data entry point of the building. A passive coupler device is attached to a centrally located service panel. The passive coupler receives the Power Line Carrier (PLC) signal from the remote entry point in the building and conditions the signal for entry at the service panel onto each phase of the three phase power distribution network.

[0001] This application claims the priority of Provisional ApplicationSerial No. 60/326,205, filed Oct. 2, 2001, the disclosure of which isexpressly incorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

[0002] The ability to interconnect computers and other intelligentdevices is a common requirement wherever people live and work today. Theelectrical connection required to form this local area network (LAN) hastraditionally been accomplished by installing dedicated data wiring bothinside buildings and between clusters of buildings. A number of wireless(i.e. radio) methods have also been developed and deployed to addressthis need.

[0003] More recently, technology to allow electric power wiringinfrastructure to simultaneously transport data at high rates has beenrealized. This Power Line Carrier (PLC) technology typically usesmodulated radio frequency (RF) signals below 50 MHz conducted on thepower wiring to transport the data.

[0004] There are significant practical advantages offered by PLCtechnology—namely that electrical wiring, of necessity, must beinstalled and that data connectivity can therefore be immediately addedat little (or no) additional cost, particularly in existing buildings.Similarly, electrical outlets are ubiquitous within modern buildings andsignificant operating convenience is realized when data issimultaneously available at every outlet.

[0005] Another advantage of PLC technology is that the range that can beachieved is significantly greater than wireless methods, particularly incommercial buildings constructed of heavier materials that severelyattenuate wireless signals. Yet another advantage of PLC technology overwireless methods is that the data is inherently more secure since aphysical connection is required to join the network.

[0006] The invention described here addresses several important problemsthat arise in the installation and use of PLC technology for local areadata networks.

[0007] Most contemporary LANs are configured in a “hub and spoke”topology where a central server device supports a number of users andalso provides a gateway to the Wide Area Network (WAN) and/or theInternet. Maximum utility for a PLC network is obtained when its'physical configuration mirrors the logical topology of the LAN, i.e.when the PLC gateway is effectively located at the “electrical center”of the space such that every outlet is served with the best possible PLCsignal. This point is often a rarely accessed electrical panel in aservice closet or the basement and is almost never co-located with otherdata processing equipment. The invention provides a simple means toremotely inject the PLC signals at this optimal point.

[0008] Another important issue, particularly in commercial buildings, isthat 3-phase electrical power/wiring is commonly used and adequatecoverage of a PLC network within the building is achieved only when allthree phases are excited with the PLC signal. The invention provides forthe simultaneous excitation of all 3 phases of power wiring with asingle PLC signal.

[0009] Yet another related issue arises during the installation of PLCnetworks in environments that have natural barriers to the signals (orblock them entirely). A common situation is where a building has beenmodified and all sections no longer share a common source of electricalpower. Another common situation is where power is supplied from acentral point and then distributed to sections of the space viatransformers, often for purposes of distribution efficiency orelectrical isolation. The invention also provides a simple and flexiblemeans to inject a single PLC signal into any number of remote points asrequired to obtain adequate coverage.

[0010] The system according to the present invention interfaces acommunicating signal with a three-phase power network of a building byfeeding a power line carrier signal to a remotely located couplingdevice which is constructed to enable each of the three phases to besupplied with the PLC signal from the remote signal source. In anotherrespect of the present invention, the signal can be fed to two or moredifferent parts of a building having different electrical isolationqualities with respect to PLC signal by providing separate couplingdevice for each part of the building.

[0011] Other objects, advantages and novel features of the presentinvention will become apparent from the following detailed descriptionof the invention when considered in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a simplified block diagram illustrating how electricalpower is supplied to and distributed within buildings.

[0013]FIG. 2 expands a portion of FIG. 1 and illustrates how and wherethe coupler constructed in accordance with the present invention ispositioned connected.

[0014]FIG. 3 is a schematic of the coupler according to the presentinvention.

[0015]FIG. 4 details an arrangement for improving PLC signal coverageand is an embodiment of the invention for buildings having portionswhich are isolated with respect to communication data.

DETAILED DESCRIPTION OF THE INVENTION

[0016] Embodiments of the current invention are directed to improvingdata connectivity afforded by PLC technology. While the carrier currentcoupler apparatus described here provides the means to effect thephysical connection to the building power wiring, much of theimprovement derives from identifying the appropriate point(s) at whichto inject the PLC signal.

[0017] One common objective is to inject the PLC signal from a single,centralized device (often called a “gateway”) into the building wiringin such a way that all receptacles in the building receive adequatesignal for a second device (often called a “terminal”) plugged in thereto function properly. The attenuation of PLC signals along arbitraryruns of wiring is difficult to predict and highly variable so it isgenerally not possible to supply all receptacles with equal signallevels. A more achievable objective is to have the building and all ofits' receptacles taken together as a system be well-behaved, i.e. whereno single receptacle is completely cut off from the PLC signal and wherethe signal amplitude decreases in a reasonably predictable fashion withdistance from the signal injection point.

[0018]FIG. 1 shows a simplified block diagram of a building powerdistribution system and will be used to illustrate the above discussion.Electricity from the utility mains enters the facility via step downtransformer (31) through terminal box (32) and is measured for billingpurposes by meter (33). It is then conducted to service panel (30) whereit is split and further directed to many receptacles (35) via panelboards (34). It is certainly possible to inject the gateway PLC signalat any of the above numbered points however the optimal point isprobably service panel (30) because it symmetrically feeds all of thereceptacles (35). PLC signal attenuated along the wiring fromtransformer (31) (if injected there) to the service panel (30) isentirely wasted since no terminal devices will ever be connected there.Similarly, injecting the gateway signal at one of the receptacles (35)could be workable but is probably not optimal since the receptacles areprobably not symmetrically distributed about any given one.

[0019] An optimized system which maximizes use of the passive couplerarrangement is to connect the carrier current coupler (20) to servicepanel (30), inject the PLC signal from gateway (40) into the building atthat point and measure the data throughput performance at a number ofreceptacles by any commonly available means. FIG. 2 illustrates thedetails of making that connection.

[0020] Referring to FIG. 2, service panel (30) is the same as discussedpreviously. Accepted electrical safety requirements prescribed in theNational Electrical Code require that a cut-off switch (22) andfuse/circuit breaker (21) be installed. Even though only minute PLCsignal currents are expected to flow along this path, the cut-off switch(22) is necessary to protect service personnel from the power linevoltage during installation/maintenance and the fuse/circuit breakerprotects the building in event of a catastrophic failure of the carriercurrent coupler (20). Terminal block (23) provides a convenientattachment point for the wiring.

[0021] An additional dimension to be considered is the common use of3-phase power in commercial buildings. In this case, service panel (30)contains 3 hot wires (often referred to as “L1”, “L2” and “L3”), aneutral and a ground wire. The object of the original building wiringplan was to balance the load across all 3 phases so roughly ⅓ of thereceptacles (35) downstream will ultimately be connected to each of L1,L2 and L3. Therefore, to provide PLC signals to all receptacles, thesignal must be split and fed to all 3 phases simultaneously. FIG. 3illustrates such connection.

[0022]FIG. 3 shows the internal details of the carrier current coupler(20). The single-ended PLC signal from the gateway is conducted viacoaxial cable (17) and subsequently coupled to each power phase viabalun transformer (14) and capacitor (12). Capacitor (13) is optionaland may or may not be used. Metal oxide varistor [MOV] (11) is used tosuppress power line transients that might cause damage to theelectronics in the gateway (40). Additional protection to the gatewayelectronics is provided by transient voltage suppressor (16). A secondfuse (15) (generally rated at very low amperage) is used to furtherprotect against short circuit failure of MOV (11). The circuit includingcapacitor (12), fuse (15) and MOV (11) is simply replicated to feed all3 phases.

[0023] If installation is completed as discussed previously andacceptable data throughput results are obtained, no further work isnecessary. On the other hand, one may find (referring once again toFIG. 1) that some receptacles (35) will not have adequate PLC signal.Assume for the purposes of this example that many of the receptacles(35) fed by one particular panel board (34) do not deliver adequate datathroughput performance. It may be possible by observation and/oranalytical means to determine why such is the case and remedy thesituation. However, details of existing wiring behind walls and/or thehistory of prior modifications made to a building may not be readilyapparent. FIG. 4 (“Multi-point PLC Signal Injection”) illustrates asolution to this problem according to another embodiment afforded by thepresent invention.

[0024]FIG. 4 shows a PLC signal simultaneously injected at some point inaddition to service panel (30) to remedy a coverage issue. Coaxialsplitter (50) is a commonly available and inexpensive device used incable TV systems to split a broadband signal for use at two or morelocations. These devices may likewise be used to split a PLC signal. Inthis example, the PLC signal output of gateway (40) along coaxial cable(17) is split and directed via individual coaxial cables (18) and (19)to two carrier current couplers (20); one installed at service panel(30) as before and another at the particular panel board (34) havingreceptacles (35) with inadequate performance. In so doing, whateverphysical issues prevented the original PLC signal from reaching thisparticular panel board are circumvented. Further, since all of the PLCsignal power still remains inside the building, the only loss is theminimal attenuation which occurs in the coaxial splitter (50) itself.The effect of this process is therefore to provide adequate signalcoverage where before there was none and to slightly reduce the signalamplitude in the rest of the space. Any number of variations of thistechnique can then be employed to address specific PLC signal coverageissues as they are subsequently discovered.

[0025] The foregoing disclosure has been set forth merely to illustratethe invention and is not intended to be limiting. Since modifications ofthe disclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

What is claimed is:
 1. A system for interfacing a communication signalwith a three phase electrical power network in a building having atleast one service panel, said system comprising: a carrier currentdevice providing a power line carrier signal; a passive coupling deviceadapted to be connected to one of said at least one service panel forcoupling said power line carrier signal to each phase of said threephase power distribution network of said building.
 2. The systemaccording to claim 1, wherein said one service panel is a service panelwhich is the most electrically centrally located service panel in saidbuilding.
 3. The system according to claim 1, wherein said passivecoupling is adapted to be coupled to a high voltage distribution systemhaving a voltage of at least 277 volts.
 4. A system for modifying apower distribution network to provide data communications, comprising: asource of data communication located at a first position and outputtinga power line carrier signal; a passive coupler directly connected to aservice location of said power distribution network for receiving saidpower line carrier signal and distributing said data on said power linedistribution network wherein said service location is remote from saidfirst location.
 5. The system according to claim 4, wherein said powerdistribution network is a three-phase power distribution network.
 6. Thesystem according to claim 4, wherein said power distribution networkincludes at least two service locations wherein said service locationdirectly connected to said passive coupler is the most centrally locatedof said at least two service locations with respect to the length ofelectrically wiring in said distribution network.
 7. The systemaccording to claim 4, wherein said passive coupler outputs a signal toeach of three phases of said power distribution system.
 8. The systemaccording to claim 4, wherein said service location is the mostelectrically centrally located service location of said powerdistribution system.
 9. The system according to claim 4, wherein saidpassive coupler is adapted to be coupled to high voltage distributionsystem having a voltage of at least 277 volts.
 10. A system forinterfacing a communication signal with each of a first portion and atleast one second portion of a power distribution network to provide datacommunication to said power distribution network, comprising: a signalsource of data communication outputting a power line carrier signal; afirst passive coupler and at least one second passive coupler whereineach of said passive couplers are directly connected to a respectiveservice location of each of said first and at least said one secondportion of said power distribution network wherein each of said firstand second portions are electrically isolated from each other withrespect to data communications and wherein each of said first and atleast one second passive couplers are connected to receive saidoutputted power line carrier signal from said signal source of datacommunication.
 11. The system according to claim 10, wherein said powerdistribution network includes three-phase power and each of said passivecouplers outputs a signal to each of said three phases.
 12. The systemaccording to claim 10, wherein each of said passive couplers is adaptedto be coupled to a high voltage distribution system having a voltage ofat least 277 volts.
 13. A method for introducing communication data intoa power distribution system of a building, comprising the steps of,generating a power line carrier signal at a first location; passivelycoupling said power line carrier signal to a service location point ofsaid power distribution system wherein said service location point isremote from said first location.
 14. The method according to claim 13,wherein said power distribution system is a three-phase system.
 15. Themethod according to claim 13, wherein the step of passively couplingsaid power line carrier signal to a service location includes the stepof passively coupling said power line carrier signal to each of threephases of said power distribution system.
 16. The method according toclaim 13, wherein said step of passively coupling said power linecarrier signal to a service location point includes the step ofpassively coupling said power line carrier signal to the mostelectrically centrally positioned service location point of said powerdistribution system.
 17. The method according to claim 16, wherein thestep of passively coupling said power line carrier signal to a servicelocation point of said power distribution system includes the step ofcoupling said power line carrier signal to a high voltage distributionsystem having a voltage of at least 277 volts.